Human herpesviruses are a diverse family of enveloped viruses that infect their hosts for life by establishing latency until virus reactivation due to immunosuppression, stress, or other cues. Herpesviruses cause a number of diseases ranging from those that are non-threatening to quite serious conditions. Non-limiting examples of herpesviruses include, HCMV, HSV-1, HSV-2, EBV, VZV, HHV-6, HHV-7, and KSHV. HCMV is a ubiquitous opportunistic pathogen that belongs to Betaherpesviridae. The virulence of this pathogen is directly linked to the immune status of its host. Primary HCMV infection is generally asymptomatic in immunocompetent individuals. After primary HCMV infection, the virus establishes lifelong latency within the host and periodically reactivates with little pathological consequences. In contrast, HCMV infection in immunocompromised patients, such as AIDS patients, and solid organ and allogeneic stem cell transplantation recipients causes serious disease (1). HCMV is also the leading cause of congenital viral infection most often resulting from a primary infection of the mother during or right before pregnancy that leads to spontaneous abortion, premature delivery, intrauterine growth restriction (IUGR), or pre-eclampsia. The risk of primary infection in a seronegative mother is 1 to 4%, which carries a 30 to 40% risk of congenital infection (2, 3). The majority of congenitally infected babies are asymptomatic at birth; however, 10 to 17% will subsequently develop hearing defects or neurodevelopmental sequelae (4).
HCMV has a double-stranded DNA genome of about 235 kb encoding about 165 genes (5). It has a very broad cellular tropism resulting in the potential infection of nearly every organ system. The ability of HCMV to enter a wide range of cell types necessitates a very complex interaction between viral envelope glycoproteins and several host cell surface receptors. The entry of herpesviruses into host cells is complex and still poorly understood. The HCMV virion envelope contains at least 20 virus-encoded glycoproteins that are involved in cell attachment and penetration (6). Of these, glycoprotein B (gB) is the most abundant glycoprotein of the HCMV envelope (7) and is highly conserved among the herpesvirus family (8). Glycoprotein B plays a critical role in the HCMV entry process where, initially, gB along with gM/gN (a complex of glycoproteins M and N), is involved in tethering of virions to heparin sulfate proteoglycans (HSPGs) on the surface of host cells. The short interactions of HCMV virions with HSPGs are followed by more stable interactions with one or more viral cellular receptors, namely EGFR (9), PDGFR (10), and TLR-2 (11). gB also interacts with integrin αvβ3, a coreceptor that enhances HCMV entry (12). Integrins are known to synergize with EGFR as well as with other receptors to activate signal transduction pathways (13-15). To complete the entry process, both viral and cellular membranes fuse, which allows the release of virion-encoded tegument and capsid proteins into the cytoplasm. This final step of viral entry into host cells requires gB and the glycoprotein H/glycoprotein L complex (16-19).
HCMV infection is highly prevalent in the population due to the ability of the virus to efficiently transmit between hosts that harbor and periodically shed the virus. HCMV is transmitted through the direct exposure to infected body secretions, including saliva, urine and milk. Following infection, HCMV enters the bloodstream and spreads to various organs including kidney, liver, spleen, heart, brain, retina, esophagus, inner ear, lungs, colon, and salivary glands (20). The ability of HCMV to infect this wide variety of cell types is not due to the presence of a high level of extracellular virus in the plasma, but it is mainly the result of cell-cell transmission between a mononuclear phagocytes, possibly a macrophage or dendritic cell precursor, and uninfected tissues (21).
Antibodies to HCMV gB have been shown to not only block penetration of virions into cells, but also to limit cell to cell infection, implying that gB plays a role in virion penetration into cells, virus transmission from cell to cell, as well as fusion of infected cells (18, 22). Recently, Isaacson and coworkers used genetic complementation to confirm that gB is required for the fusion of viral and cellular membranes, virus entry, and cell-to-cell spread of HCMV (23).
Since HCMV and other herpesviruses establish a lifelong latency in humans, antiviral therapy that inhibits viral entry may serve as an alternative to the already existing therapeutic agents. Here, we report the design and development characterization of peptides that specifically inhibit the fusion of HCMV to the host cell membrane to inhibit viral infection and/or replication as a novel approach to prevent HCMV infection.